Effects of cow's and goat's milk as fermentation media on the microbial ecology of sugary kefir grains

In the present study, we have investigated the importance of fermentation media on grain formation and the microbial characteristics of sugary kefir. The sugary kefir grains were fermented in brown sugar, cow's milk or goat's milk. Using culture-dependent and culture-independent methods, we identified the microorganisms present in both the grains and filtrate and then evaluated their distribution. The structure of the grains was also observed by scanning electronic microscopy (SEM). The identification results indicated that there were remarkable changes in microbial ecological profiles of the sugary kefir grains and their filtrates when brown sugar and milk were compared as fermentation media. Three lactic acid bacteria (LAB) species (Leuconostoc mesenteroides, Lactobacillus mali and Lactobacillus hordei) were found in the grains fermented using brown sugar. However, four species, named Leu. mesenteroides, Lactococcus lactis, Bifidobacterium psychraerophilum and Enterococcus faecalis, were identified in the grains fermented using either cow's or goat's milk. The size and structure of the kefir grains were also significantly influenced by the culture medium. We hypothesize that the grains originally may contain many different microorganisms and the identified changes are an adaption to each specific medium during grain formation and growth. The distribution of strains thus may vary depending on the carbon and energy sources available for grain fermentation and these microbial changes will further affect the granulation and growth of the grains. This study is important to our understanding of the mechanism of kefir grain formation and growth because it explores the relationship between fermentation media and kefir microorganisms.

► This study is important in understanding the mechanism of kefir grain formation and growth because it explores the relationship between fermentation media and the kefir microorganisms. ► Two unusual LAB strains, Lactobacillus hordei and Lactobacillus mali, were identified for the first time in the brown sugar kefir grain samples. ► Based on our findings, we propose that the grains originally contain many different microorganisms that are able to adapt to different environments during grain formation and growth.